In the past, difficulty has been experienced when pouring liquids by hand from containers, especially when the containers are fairly large and full and when dealing with flammable, highly viscous and other liquids which are difficult to handle. The efflux of liquid from the container can be too sudden or irregular due to a flow interruption phenomenon known as "glugging" caused by large air bubbles entering the container at slow speeds with resultant surges in flow rate. This leads to spillage on persons, clothing or equipment.
Metallic closure caps have largely been replaced by plastic caps and particularly those of so-called "yieldable" plastics material because of greater durability and ease of manufacture by injection moulding techniques. Resilient, two-piece, screw on, captive caps of plastic material for fitment to containers for dispensing liquids thereform through a closable opening are known wherein the cap is rotated in a clockwise direction to close the discharge opening and in an anti-clockwise direction to open the discharge opening. Many captive, screw-on caps are of the snap-fit variety and are not removable from the container by a consumer without damage. Effective sealing of the surfaces of closure caps either with containers or insert members is a problem. Some rotatable, screw-valve, captive plastic caps rely on deformation and distortion of the wall of an outer sleeve or tubular member by the user during placement of a captive cap upon the container. The sleeve usually has an internal annular flange on the bottom edge which engages with an external annular flange or lip on the container neck. Examples of this type of closure are disclosed in U.S. Pat. No. 1,977,537 of Warmuth, U.S. Pat. No. 2,051,513 of Bingham and U.S. Pat. No. 2,969,896 of Lerner. In all of these patents, the whole cap is rotated and use is made of the rim of the container neck as a sealing surface. Other caps, such as those in U.S. Pat. No. 3,216,630 and U.S. Pat. No. 3,351,249 of Stull, rely on radial distortion of an upper edge of a wall of a resilient tubular sleeve member to free an annular sealing surface bead of a closure cap from an internal annular groove in the wall each time that the cap is screwed open or closed for axial movement. This type of closure can be assembled during manufacture by axial snap-fitting movement over-riding the threads instead of a rotary movement. In another closure type described in U.S. Pat. No. 3,033,428 of Van Baarn, distortion and deformation of resilient sealing members is used during closure movement to prevent sticking of sealing members due to residual amounts of material dispensed from a container with liquid to which the closure has been fitted. In another U.S. Pat. No. 3,276,640 of Kessler, distortion for fitment is achieved by having a central, resilent plug, (integral with an axially slidable cap and plunger) of double taper and with a blind bore in the bottom, the plug being forced past an internal flange on an unthreaded tubular, sleeved pouring spout. In U.S. Pat. No. 3,606,105 of Santore, a screw-on cap moves axially and uses direct sealing against the upper rim or edge of a squeeze container dispenser and dispensing relies partly on the container structure and material rather than the closure.